Running a pike as a lib inside another could theoretically work if the embedding interface is developed more. Right now I think there would be too many symbol conflicts.
But it'd be very cumbersome to use. Since the two interpreters would be completely separate, the only way to pass data between them would be through pipes or the shared memory interface, which only can pass strings. You could just as well run several pike processes.
The planned multi-cpu support aims a lot higher than that. You're welcome to read the preliminary spec here: http://pike-git.lysator.liu.se/gitweb.cgi?p=pikex.git;a=blob_plain;f=multi-c... Feedback is welcome.